Processes for making detergent range alkylbenzenes

ABSTRACT

Spent benzene from a regeneration of a catalyst or solid sorbent in an alkylbenzene complex is subjected to a rough distillation and the benzene fraction from the rough distillation is used a at least a portion of the benzene for a unit operation in the alkylbenzene complex or is passed to a benzene distillation column in the crude alkylbenzene refining section. The processes of this invention can enhance the purity of the alkylbenzene product and can reduce energy consumption per unit of alkylbenzene product or can assist in debottlenecking the crude alkylbenzene refining section of the alkylbenzene complex.

FIELD OF THE INVENTION

This invention pertains to integrated processes using solid, acidiccatalysts for benzene alkylation to make detergent range alkylbenzenesof enhanced quality. The integrated processes of this invention alsoenable the operation of an alkylbenzene complex with improved energyefficiency. In the processes of this invention, benzene used for atleast one of regeneration of catalyst or solid sorbent is subjected tofractionation by a rough distillation to remove higher boilingimpurities.

BACKGROUND TO THE INVENTION

Alkylation of benzene produces alkylbenzenes that may find variouscommercial uses, e.g., alkylbenzenes can be sulfonated to producedetergents. Alkylbenzenes are produced as a commodity product inlarge-scale facilities, e.g. often in amounts of 50,000 to 200,000metric tonnes per year per plant. In the alkylation process, benzene isreacted with an olefin the desired length to produce the soughtalkylbenzene. The alkylation conditions comprise the presence ofhomogeneous or heterogeneous alkylation catalyst such as aluminumchloride, hydrogen fluoride, silica alumina or zeolitic catalysts andelevated temperature.

The alkylbenzene must meet stringent product specifications to becommercially acceptable. For instance, alkylbenzenes, to be desirablefor making sulfonated surfactants, must be capable of providing asulfonated product of suitable clarity, biodegradability and efficacy.The benzene content of the product should be relatively free frombenzenes, e.g., less than about 1 part per million by weight (ppmw), andoften less than about 0.5 ppmw. Additional considerations for commercialalkylbenzene products include the 2-phenyl content and linearity of thealkyl substituent.

An important property of alkylbenzene as a feed for making a sulfonatedsurfactant is that it not impart undue color to the sulfonated product.Thus, the alkylbenzenes should have an absence of color formers, orcolor bodies. Color bodies are components that impart color to thealkylbenzene. Saybolt color is one procedure for determining color of aliquid and for purposes herein refers to ASTM D-156-00, Standard TestMethod for Saybolt Color of Petroleum Products (Saybolt ChronometerMethod), which is in effect on Jul. 31, 2004, available from ASTMInternational. Desirable alkylbenzenes have a Saybolt color of at least+25, and preferably at least +29.

In the process for making alkylbenzene using a solid, acidic catalyst,benzene is alkylated with an olefin under alkylation conditions. A highbenzene to olefin ratio is used in part to reduce side reactions thatgenerate heavies and in part to serve as a heat sink for the alkylationreaction. Typically, alkylbenzene is purified by the use of severaldistillation steps. For instance, see Pujado, Linear Alkylbenzene (LAB)Manufacture, Handbook of Petroleum Refining Processes, Second Edition,pp 1.53 to 1.66 (1996), especially pages 1.56 to 1.60. In general, thealkylation reaction product is subjected to a first distillation in abenzene column to separate benzene as an overhead stream that can berecycled to the alkylation reaction. The bottoms stream from the benzenecolumn is then subjected to a distillation to separate paraffins andunreacted olefin in a paraffins column. The paraffins-containingoverhead is capable of being recycled to a paraffin dehydrogenation unitwhile the bottoms stream is passed to a heavy alkylate distillationcolumn. In the heavy alkylate distillation column, heavies are separatedfrom the lighter alkylbenzene, and a heavies-containing stream iswithdrawn as a bottoms stream. If desired, the bottoms stream can besubjected to a further distillation to recover additional alkylbenzene.

Benzene also finds other applications in an alkylbenzene complex. Forinstance, the solid, acidic catalyst must be periodically regenerated.The regeneration is effected by passing benzene over the catalyst atelevated temperature to remove deactivating components. Another use forbenzene is where the olefin-containing feed is subjected to selectivesorption to remove unwanted aromatic compounds, and benzene is used toregenerate the selective sorbent. See, for instance, U.S. Pat. No.6,740,789. If the alkylbenzene complex provides for transalkylation ofheavies over a solid catalyst, then benzene may also find use inregenerating the transalkylation catalyst.

Efficient use of benzene is required for commercially viablealkylbenzene complexes. Thus, benzene must be recycled. Proposals havebeen made to effectively use the benzene by cycling it through two ormore unit operations in the alkylbenzene production complex. See, forinstance, U.S. Pat. No. 6,740,789. Hence benzene management in thealkylbenzene production complex involves not only the alkylationreaction but also a plurality of other uses. Typically, therefore, spentbenzene from such regenerations is returned to the benzene column forthe purification of crude alkylbenzene. The benzene column, togetherwith make-up benzene, provides benzene for the alkylation as well at theregeneration uses.

SUMMARY OF THE INVENTION

In accordance with this invention it has been found that the quality ofthe alkylbenzene can be enhanced where the spent benzene from aregeneration has been subjected to a fractionation by a roughdistillation to remove higher boiling components. In one broad aspect ofthe invention, at least a portion of the benzene stream from this roughdistillation is directly or indirectly introduced into a benzene columnused for the refining of crude alkylbenzene. In another broad aspect, atleast a portion of the benzene stream from this rough distillation isused for regeneration. A rough distillation, as used herein, is adistillation using up to 2, preferably up to 1, theoretical distillationplates. Often the rough distillation has no reflux.

Despite the lack of separation capability of the rough distillation, notonly can alkylbenzene products of enhanced quality be obtained but also,the benzene fraction provided by the rough distillation is of adequatequality for other uses in the alkylbenzene complex, including, but notlimited to, alkylation catalyst regeneration, transalkylation catalystregeneration (if used), regeneration of selective sorbent used to treatthe olefin-containing feed for the alkylation, and as a feed for atransalkylation of heavies (if used). A particularly attractive use ofthe benzene stream from the rough distillation is for regeneration. Notonly is the benzene stream of adequate quality for the regeneration ofalkylation catalyst and selective sorbent, but also, the benzene streamis obtained with less reboiler duty than an equivalent amount of benzenefrom the benzene column for refining the crude alkylbenzene product. Asthe benzene column for refining the crude alkylbenzene product mustremove paraffins from the benzene, substantial reflux ratios are used ineffecting the fractionation. The relative absence of paraffins in thespent benzene from the regeneration, together with the deactivatingcomponents typically being higher molecular weight species, enables therough distillation to be conducted with little, if any, reboiler duty,especially since regeneration is typically conducted at elevatedtemperatures.

In a preferred aspect, the processes of this invention enable a secondbenzene loop to be established, the first being the loop with thealkylation reaction and the benzene column for refining the crudealkylbenzene, and the second being the loop with the catalyst or sorbentand the rough distillation.

In a broad aspect of the invention, continuous, integrated processes areprovided for preparing linear alkylbenzenes by the alkylation of benzenewith olefin having between about 8 and 16, preferably between about 9and 14, carbon atoms, said olefin being contained in admixture withparaffin, in the presence of regenerable, solid, acid alkylationcatalyst comprise:

a. continuously supplying benzene and a mixture of said olefin andparaffin to alkylation conditions in at least one alkylation zone of atleast two alkylation zones including the presence of a catalyticallyeffective amount of said catalyst to provide an alkylation productcontaining alkylbenzene and unreacted benzene, wherein said alkylationdeactivates said catalyst;

b. separating benzene from the alkylation product to provide abenzene-rich fraction, at least a portion of which is recycled to step(a) and a substantially benzene-free fraction, said fraction containingalkylbenzene and paraffin;

c. separating paraffin from said substantially benzene-free fraction toprovide a paraffin-rich fraction and a substantially paraffin-freefraction containing alkylbenzene;

d. periodically regenerating said catalyst in at least one of saidalkylation zones by continuously passing through said zone benzene underregeneration conditions to provide a spent benzene-containingregeneration stream which also contains deactivating components removedfrom the catalyst; and

e. fractionating at least a portion of the spent benzene-containingregeneration stream by rough distillation benzene from deactivatingcomponents to provide a lower boiling benzene-containing streamcontaining less than about 1, preferably less than about 0.5, masspercent hydrocarbons having at least 12 carbon atoms.

The fractionation of step (e) provides a higher boiling fraction thatcontains deactivating components. Often the higher boiling fraction willcontain benzene due to the nature of the rough distillation. Generallythe benzene is present in the higher boiling fraction in an amount lessthan about 70, preferably less than about 50, mass percent. The lowerboiling benzene stream from step (e) may be used in one or more ways. Atleast a portion of the lower boiling benzene stream from step (e) can bepassed to step (b). As deactivating components, some of which may becolor formers, are removed, such components are not introduced into thealkylbenzene refining system where they may not be effectively separatedfrom the alkylbenzene or may react under the conditions of theseparations in the refining system to provide components that areundesirable in the alkylbenzene product.

Also where the mixture of olefin and paraffin for step (a) is derivedfrom the dehydrogenation of paraffin and a selective sorbent is used toremove aromatic compounds from the olefin and paraffin mixture prior tostep (a) and at least a portion of the lower boiling benzene stream fromstep (e) can be used to regenerate the selective sorbent. Not only canthis reuse of benzene reduce the amount of benzene that must bedistilled in step (b) per unit of alkylbenzene product, but also, theremoval of deactivating components by the rough distillation preventsany undue adverse effect to the selective sorbent.

At least a portion of the lower boiling benzene may be used as at leasta portion of the benzene feed for a transalkylation of heavies. In thisembodiment,

i. the alkylation product of step (a) contains dialkylbenzene and thesubstantially paraffin-free fraction containing alkylbenzene of step (c)contains alkylbenzene and dialkylbenzene;

ii. said paraffin-free fraction is further separated to provide analkylbenzene fraction substantially devoid of dialkylbenzenes and aheavies fraction containing dialkylbenzenes; and

iii. at least a portion of the heavies fraction to transalkylationconditions comprising the presence of a catalytically effective amountof solid transalkylation catalyst and benzene, at least a portion ofwhich is provided from the lower boiling benzene fraction from step (e),to provide a transalkylation product containing alkylbenzene andunreacted benzene.

In another preferred embodiment of the invention, at least a portion ofthe lower boiling benzene from step (e) is passed to step (a) as aportion of the benzene feed for alkylation. In this embodiment, thebenzene used for the regeneration of the solid, acidic catalyst isrelatively devoid of paraffin and with the removal of deactivatingcomponents in the rough distillation, the benzene can be used withoutuntoward effects for the alkylation reaction.

In another preferred embodiment of the invention, at least a portion ofthe lower boiling benzene from step (e) can be recycled to step (d) forregeneration of solid, acidic catalyst. As the benzene required forregeneration of solid, acidic catalyst used for the alkylation oftenconstitutes 20 to 25 mass percent of the benzene from step (b), theability to recycle spent benzene stream to the catalyst regenerationresults in an energy savings since the distillation is be a crudedistillation and not the more extensive distillation provided by thebenzene column for refining crude alkylbenzene which has a high heatduty due to the significant reflux ratio required to separate paraffins.Further, by establishing a second benzene cycle, capacity of the benzenecolumn for refining the crude alkylbenzene can be reduced, or for anexisting alkylbenzene complex, alkylbenzene production capacity can beincreased.

A particularly attractive use of the processes of this invention takesinto account the composition of the spent benzene stream from aregeneration. For instance, the regeneration of step (d) typicallycomprises (i) a purge stage during which the catalyst is flushed, (ii) aheating stage during which the temperature is increased to that suitablefor regeneration, (iii) a regenerating stage during which deactivatingcomponents are removed from the catalyst, and (iv) a cool down stageduring which the catalyst is cooled to a temperature suitable for use instep (a). Preferably at least the spent benzene stream from step (iii)is passed to step (e). The spent benzene stream from step (i) willcontain paraffins and potentially some olefins and virtually nodeactivating components. It may be recycled to step (a) without thefractionation of step (e). Or, if a transalkylation unit operation isused, then this spent benzene regenerant may be used as a portion of thebenzene feed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an alkylbenzene complex usingthe processes of this invention.

FIG. 2 is a schematic representation of an alkylation reactor assemblysuitable for use in the alkylbenzene complex of FIG. 1.

FIG. 3 is a schematic representation of a transalkylation assemblysuitable for use in the alkylbenzene complex of FIG. 1.

Parameters

Color

As used herein, color bodies are components of a mixture that impartcolor to the mixture, and Saybolt color refers to Saybolt color asdetermined by ASTM D-156-00, Standard Test Method for Saybolt Color ofPetroleum Products (Saybolt Chronometer Method), which is available fromASTM International, 100 Barr Harbor Drive, P.O. Box C700, WestConshohocken, Pa., USA.

Linearity

As used herein, linearity is the mass percent of normal alkylbenzenes tototal alkylbenzenes.

Bromine Index

There are a number of methods for determining a bromine index of analkylbenzene, but the methods often provide results that are notconsistent with each other. Hence, for purposes herein, the bromineindex is that measured by UOP Method 304-90, “Bromine Number and BromineIndex of Hydrocarbons by Potentiometric Titration”, which is in effecton Jul. 31, 2004, available from ASTM International.

2-Phenyl Content

The 2-phenyl content of an alkylbenzene is the mass percent of thealkylbenzene that is a 2-phenylalkane.

DETAILED DISCUSSION

Various processes have been proposed for the alkylation of benzene. See,for instance, Pujado, Linear Alkylbenzene (LAB) Manufacture, Handbook ofPetroleum Refining Processes, Second Edition, pp 1.53 to 1.66 (1996).One type of process uses a solid acidic catalyst involving contacting anolefin with a stoichiometric excess of benzene at elevated temperatureto produce alkylbenzene. The reaction product stream will contain, inaddition to alkylbenzene, benzene, some unreacted olefin, and reactionbyproducts such as dialkylbenzene and oligomers and polymers of theolefin. For commercial processes, the feedstocks may include othercomponents as well. For instance, the olefin may be obtained by thedehydrogenation of a paraffinic feedstock and thus contain significantamounts of paraffin.

The Olefin-Containing Feedstock

Olefin-containing aliphatic compound and benzene are used for thealkylation process. The selection of the olefin is dependent upon thesought alkylation product. The olefin-containing aliphatic compound ispreferably has between about 8 and 16, and for detergent applications 9to 14, carbon atoms. The olefin-containing aliphatic compound is anacyclic, mono-olefinic compound. The positioning of the olefinic bond inthe molecule is not critical as most alkylation catalysts have beenfound to promote migration of the olefinic bond. However, the branchingof the hydrocarbon backbone is often more of a concern as the structuralconfiguration of the alkyl group on the alkylbenzene product can affectperformance especially in surfactant applications and for biodegradationproperties. For instance, where alkylbenzenes are sulfonated to producesurfactants, undue branching can adversely affect the biodegradabilityof the surfactant. On the other hand, some branching may be desired suchas the lightly branched modified alkylbenzenes such as described in U.S.Pat. No. 6,187,981. The olefin may be unbranched or lightly branched,which as used herein, refers to an olefin having three or four primarycarbon atoms and for which none of the remaining carbon atoms arequaternary carbon atoms. A primary carbon atom is a carbon atom which,although perhaps bonded also to other atoms besides carbon, is bonded toonly one carbon atom. A quaternary carbon atom is a carbon atom that isbonded to four other carbon atoms. Although branched, thesealkylbenzenes have been characterized by their 2-phenyl content, see forinstance, U.S. Pat. No. 6,589,927.

The olefin-containing aliphatic compound is usually a mixture of two ormore olefins. For commercial processes, the feedstocks may include othercomponents as well such as aromatics, lighter mono-olefins, diolefins,paraffins, halogenated hydrocarbons, and oxygenated hydrocarbons such asaldehydes, ethers, esters and carboxylic acids. For instance, the olefinmay be obtained by the dehydrogenation of a paraffinic feedstock andthus contain paraffin. Of course, other olefin synthesis procedures suchas dehydration of alcohols and dechlorination, can provide theolefin-containing feedstock. Feedstocks from such sources may havelittle, if any, paraffin.

The paraffin is inert in the alkylation reaction but it can serve animportant function as a heat sink as the alkylation reaction isexothermic. Where lower benzene to olefin feed ratios are used, theimportance of paraffins as heat sinks to adsorb the heat of thealkylation reaction, becomes more important. Nevertheless, in the broadaspects of the processes of this invention, the olefin may be in anyconcentration in the feedstock including substantially pure. Often,however, the feedstock comprises at least about 5 or 10 mole percentolefin. Especially where the feedstock is from the catalyticdehydrogenation of paraffin, the olefin is usually in an amount of about5 to 30, and more frequently about 9 to 20, mass-percent of thefeedstock.

Where the olefin is obtained by the dehydrogenation of paraffin, thesource of the paraffinic feedstock is not critical although certainsources of paraffinic feedstocks will likely result in the impuritiesbeing present. Conventionally, kerosene fractions produced in petroleumrefineries either by crude oil fractionation or by conversion processestherefore form suitable feed mixture precursors. Fractions recoveredfrom crude oil by fractionation will typically require hydrotreating forremoval of sulfur and/or nitrogen prior to being fed to the subjectprocess. The boiling point range of the kerosene fraction can beadjusted by fractionation to adjust the carbon number range of theparaffins. In an extreme case the boiling point range can be limitedsuch that only paraffins of a single carbon number predominate. Kerosenefractions contain a very large number of different hydrocarbons and thefeed mixture to the subject process can therefore contain 200 or moredifferent compounds.

The paraffinic feedstock may be at least in part derived fromoligomerization or alkylation reactions. Such feed mixture preparationmethods are inherently imprecise and produce a mixture of compounds. Thefeed mixtures to the process may contain quantities of paraffins havingmultiple branches and paraffins having multiple carbon atoms in thebranches, cycloparaffins, branched cycloparaffins, or other compoundshaving boiling points relatively close to the desired compound isomer.The feed mixtures to the process of this invention can also containaromatic hydrocarbons.

Another source of paraffins is in condensate from gas wells. Usuallyinsufficient quantities of such condensate are available to be theexclusive source of paraffinic feedstock. However, its use to supplementother paraffinic feedstocks can be desirable. Typically thesecondensates contain sulfur compounds, which have restricted their use inthe past. As this invention enables the use of sulfur-containing feeds,these condensates can be used to supply paraffins for alkylation.

Paraffins may also be produced from synthesis gas (Syngas), hydrogen andcarbon monoxide. This process is generally referred to as theFischer-Tropsch process. Syngas may be made from various raw materialsincluding natural gas and coal, thus making it an attractive source ofparaffinic feedstock where petroleum distillates are not available. TheFischer-Tropsch process is a catalytic process conducted under elevatedtemperature and pressure. The reaction is temperature sensitive, andtemperature control is essential to achieve a desired hydrocarbonproduct. The products from the Fischer-Tropsch process include not onlyparaffins but also monoolefins, diolefines, aromatics and oxygenatessuch as alcohols, ethers, aldehydes and ketones, and thus are normallytreated to eliminate oxygenates.

The olefin-containing feedstock should be sufficiently free ofimpurities that can unduly adversely affect the life of the alkylationcatalyst and that can adversely affect the quality of the alkylbenzeneproduct. The dehydrogenation of paraffins will result in a productcontaining aromatics, herein referred to as aromatic by-products. Thearomatic by-products can comprise substituted phenyl compounds such astoluene, xylenes, and higher methylated benzenes; ethylbenzene,diethylbenzene, and triethylbenzenes; isopropylbenzene (cumene),n-propylbenzene, and higher propylbenzenes; butylbenzenes; andpentylbenzenes and the like; biphenyl compounds and substituted biphenylcompounds; and fused ring compounds and substituted fused ring compoundssuch as napthalenes, indanes, tetralins, and the like. Where thefeedstocks are used to make alkylbenzenes and a paraffin-containingstream is generated during the purification of the alkylbenzenes and isrecycled to the dehydrogenation, the feedstocks may also containalkylbenzenes. In many instances, the aromatic by-products have the samecarbon number as the mono-olefins. The concentration of the aromaticby-products can vary widely, e.g., from about 0.3 to 10 mass-percentbased upon the mass of the feedstock.

Advantageously at least a portion of the aromatic by-products in themono-olefin-containing feedstock is removed using at least one aromaticsremoval zone. An aromatics removal zone may be placed in one or morelocations. For instance, where the feedstock is obtained from acatalytic dehydrogenation including a selective diolefin hydrogenationzone, the aromatic by-products may be selectively removed before orafter the selective hydrogenation.

Suitable aromatics removal zones for this embodiment of the inventioninclude sorptive separation zones. Sorptive separation zones includefixed bed or moving or fluidized sorbent bed systems, but the fixed bedsystem is preferred. The sorbent may be installed in one or more vesselsand in either series or parallel flow. The flow of the feedstockcontaining the aromatic by-products through the sorptive separationzones is preferably performed in a parallel manner so that one or moresorption beds can be undergoing regeneration while one or more beds areremoving aromatic by-products.

Suitable sorbents may be selected from materials which exhibit theprimary requirement of selectivity for the aromatic by-products andwhich are otherwise convenient to use. Suitable sorbents include, forexample, molecular sieves, silica, activated carbon activated charcoal,activated alumina, silica-alumina, clay, cellulose acetate, syntheticmagnesium silicate, macroporous magnesium silicate, and/or macroporouspolystyrene gel. It should be understood that the above-mentionedsorbents are not necessarily equivalent in their effectiveness. Thechoice of sorbent will depend on several considerations including thecapacity of the sorbent to retain aromatic by-products, the selectivityof the sorbent to retain the aromatic by-products which are moredetrimental to solid alkylation catalysts, and the cost of the sorbent.The preferred sorbent is a molecular sieve, and the preferred molecularsieve is 13 X zeolite (sodium zeolite X).

Those skilled in the art are able to select the appropriate conditionsfor operation of the sorbent without undue experimentation. For example,a fixed bed sorptive separation zone containing 13 X zeolite may bemaintained at a temperature generally from about 20° C. to 300° C., andpreferably from about 100° C. to 200° C., a pressure effective tomaintain the stream containing the aromatic by-products in a liquidphase at the chosen temperature, and a liquid hourly space velocity fromabout 1 hr⁻¹ to about 10 hr⁻¹ and preferably from about 1 hr⁻¹ to about3 hr⁻¹. The flow of the feedstock through a fixed or moving sorption bedmay be conducted in an upflow, downflow or radial-flow manner.

Although both liquid and vapor phase operations can be used in manysorptive separation processes, liquid phase operation is preferred forthe sorptive separation zone because of the lower temperaturerequirements and because of the higher sorption yields of the aromaticby-products that can be obtained with liquid phase operation over thoseobtained with vapor phase operation. Therefore, the temperature andpressure of the sorptive separation are preferably selected to maintainthe feedstock in a liquid phase. The resulting unsorbed stream having areduced concentration of aromatic by-products is a desorption effluent.However, the operating conditions of a sorptive separation zone can beoptimized by those skilled in the art to operate over wide ranges whichare expected to include the conditions in the reaction zones of theinvention and its variants. Therefore, a sorptive separation zone may becontained in a common reaction vessel with the dehydrogenation zone, theselective diolefin hydrogenation zone, or the selective alkylation zone.

A sorbent bed is periodically subjected to regeneration conditions. Abenzene-containing stream is use for the regeneration. Generally it ispreferred that the benzene be highly pure to avoid undue sorption of anyimpurities on the sorbent during regeneration. Nevertheless, theregenerant may contain components that do not materially interfere withthe regeneration and are acceptable in the sorption effluent. Forintegrated processes where the sorption effluent is used as a feed to abenzene alkylation reactor and benzene from the refining system is usedas regenerant, to prevent undue buildup of paraffins in the regenerationeffluent distillation system, the regenerant should contain less than0.1 mass-percent paraffins, more preferably less than 100 mppm (masspart per million) paraffins. Typically the regenerant contains at leastabout 50, preferably at least about 90 or 99, more preferably to atleast 99.5, to essentially 100, mass-percent benzene. A purge may beintermittently or continuously withdrawn from at least one point in therecycle loop consisting of the sorber assembly and the regenerationeffluent distillation system in order to avoid excessive concentrationsof paraffins. Where the sorption effluent is used as a feed to analkylation reactor to make alkylbenzene, the regenerant is convenientlya pure benzene stream from the refining of the alkylbenzene-containingreaction effluent. Any suitable regeneration method may be used,including altering the temperature and pressure of the sorbent andtreating with liquid or vaporous or mixed phase regenerant to displaceor desorb aromatic by-products.

The spent benzene from the regeneration of the sorbent may be recycledto the alkylbenzene refining system or may be treated as disclosed incopending U.S. patent application Ser. No. 11/313071, filed Dec. 20,2005, herein incorporated by reference in its entirety.

The Alkylation

In the alkylation step, benzene and olefin feedstock are reacted underalkylation conditions to provide an alkylbenzene product. Alkylationconditions include the presence of a solid, acidic catalyst. Thealkylation conditions selected will affect the nature of thealkylbenzene product as well as the conversion and selectivity toalkylbenzenes. For instance, higher alkylation temperatures can reducethe linearity of the alkylbenzene product and the type of catalyst canaffect the 2-phenyl content of the alkylbenzene product. The benzene toolefin mole ratio is a major determinant of the extent of heaviesgenerated during the alkylation. In general, the greater thestoichiometric excess of benzene, the greater the selectivity toalkylbenzene. Typically, the ratio of benzene to olefin duringalkylation is within the range of about 5:1 to 50:1 or more, oftenbetween about 10:1 to 30:1.

Alkylation conditions generally include a temperature in the rangebetween about 80° C. and about 200° C., most usually at a temperaturenot exceeding about 175° C. Since the alkylation is typically conductedin at least partial liquid phase, and preferably in either an all-liquidphase or at supercritical conditions, pressures must be sufficient tomaintain benzene as a liquid. The requisite pressure necessarily dependsupon the temperature, but normally is in the range of about 1300 to 7000kPa(g), and most usually between about 2000 and 3500 kPa(g). Preferablythe alkylation conditions do not result in substantial skeletalisomerization of the olefin. For instance, less than 15 mole percent,and preferably less than 10 mole percent, of the olefin, the aliphaticalkyl chain, and any reaction intermediate undergoes skeletalisomerization.

Any suitable alkylation catalyst may be used in the present invention,provided that the requirements for conversion, selectivity, and activityare met. Alkylation catalysts comprise zeolites having a zeolitestructure type selected from the group consisting of FAU, BEA, MOR, MTW,and NES. Such zeolites include mordenite, ZSM-4, ZSM-12, ZSM-20, ZSM-38,MCM-22, MCM-36, MCM-49, UZM-8, offretite, gmelinite, zeolite Y, NU-87,and gottardite. Another class of acidic, solid catalyst components areacidified refractory oxides such as chlorided, fluorided, or sulfatedalumina, gallia, boria, molybdia, ytterbia, titania, chromia, silica,zirconia, and the like and combinations thereof. Clays and amorphouscatalysts may also find utility. Further discussion of alkylationcatalysts can be found in U.S. Pat. Nos. 5,196,574; 6,315,964 and6,617,481.

The catalyst may contain suitable binder or matrix material such asinorganic oxides and other suitable materials. The relative proportionof molecular sieve or other catalytically active component in thecatalyst may range from about 10 to about 99 mass-percent, with about 20to about 90 mass-percent being preferred. A refractory binder or matrixcan be used to facilitate fabrication of the catalyst, provide strengthand reduce fabrication costs. The binder should be uniform incomposition and relatively refractory to the conditions used in theprocess. Suitable binders include inorganic oxides such as one or moreof alumina, magnesia, zirconia, chromia, titania, boria and silica. Thecatalyst also may contain, without so limiting the composite, one ormore of (1) other inorganic oxides including, but not limited to,beryllia, germania, vanadia, tin oxide, zinc oxide, iron oxide andcobalt oxide; (2) non-zeolitic molecular sieves, such as thealuminophosphates of U.S. Pat. No. 4,310,440, thesilicoaluminophosphates of U.S. Pat. No. 4,440,871 and ELAPSOs of U.S.Pat. No. 4,793,984; and (3) spinels such as MgAl₂O₄, FeAl₂O₄, ZnAl₂O₄,CaAl₂O₄, and other like compounds having the formula MO—Al₂O₃ where M isa metal having a valence of 2; which components can be added to thecomposite at any suitable point.

Alkylation of benzene by the olefins is conducted in a continuousmanner, i.e., both the benzene and the olefin-containing feedstock arecontinuously introduced into the alkylation zone containing the catalystbed. For purposes herein, a catalyst bed is termed a reactor whether inthe same or a separate vessel from another bed. The catalyst may be usedas a packed bed or a fluidized bed. The feed to the reaction zone may bepassed either upflow or downflow, or even horizontally as in a radialbed reactor. In one desirable variant, olefin-containing feedstock maybe fed into several discrete points within the reaction zone.

One or more alkylation zones can be used. The alkylation zones may beconfigured in parallel with the same or different catalyst in each.Alkylation zones may also be configured in series, especially with aportion of the olefin-containing feedstock being fed to two or morealkylation zones. The benzene may be fed to the first reaction zonethereby providing a high benzene to olefin ratio in that zone, and thealkylation product is then fed, with additional olefin-containingfeedstock to a subsequent reaction zone. Often 3 reactors are used toachieve an advantageous combination of performance and capital expenseavoidance with one alkylation reaction zone being off-line forregeneration.

Where a low benzene to olefin ratio is used, there is less benzene toadsorb the heat of the alkylation reaction. As higher alkylationtemperatures can result in loss of linearity of the alkylbenzene productcan occur. It may be desired to use a plurality of alkylation zones withcooling there between. For instance, benzene and a portion of the olefinfeedstock at a first blend temperature can be passed to a first zonewhere the mass ratio of benzene to olefin feedstock is sufficient thatthe temperature of the first zone effluent is less than 15° C.,preferably less than about 12° C., and most preferably less than about10° C., above the blend temperature; the first zone effluent is cooledand combined with another portion of the aliphatic feedstock at a secondblend temperature. This mixture is passed to a second reaction zone toproduce a second zone effluent comprising alkylbenzene and the massratio of benzene to olefin feedstock is sufficient that the temperatureof the second zone effluent is less than 15° C., preferably less thanabout 12° C., and most preferably less than about 10° C., above theblend temperature. This technique can be repeated a sufficient number oftimes to use the olefin feedstock.

The cooling of each zone effluent may be by direct or indirect heatexchange, and is preferably at least partially effected by direct heatexchange with the portion of the olefin feedstock being passed to thezone, the olefin feedstock being provided at a cooler temperature thanthe preceding zone effluent. The cooling is often sufficient to reducethe temperature increased experienced in the previous reaction zone byat least 60 percent, and preferably the temperature reduction is atleast to that of the blend temperature of the previous reaction zone.

A trim reaction zone containing solid alkylation catalyst can be used inany alkylation reaction scheme. The trim reaction zone does not receiveany portion of the aliphatic feedstock but rather is maintained underliquid phase alkylation conditions sufficient to consume substantiallyall olefin contained in the zone effluent from the last of the zones.

Another technique is to remove at least a portion of the alkylbenzenebetween alkylation zones to reduce the production of dialkylbenzenes.The separation may be by any convenient means including membraneseparation, selective sorption and distillation. In one technique alights distillation is used to recover a portion of the unreactedbenzene contained in the effluent from an alkylation reaction zone. Thebenzene is recycled to the alkylation zone, and the remaining portion ofthe unreacted aromatic compound is recovered in a subsequentdistillation. The column size and energy requirements for the subsequentdistillation are thus reduced. Because the lights distillation need notprovide a relatively pure aromatic stream, the energy requirements andsize of the lights distillation can be commercially viable. Often, thelights distillation is effected using less than 5 theoreticaldistillation trays, especially a flash distillation. Thus, the overheadcan contain appreciable amounts of alkylbenzene product as well asparaffins, if paraffins are present in the alkylation reactor effluent.Although arylalkane can be reacted to produce heavies under alkylationconditions, the processes of this invention can still provide analkylation reaction effluent without an undue amount of heavies.Advantageously, the distillation is conducted at a lower pressure thanthe alkylation zone, and is often at between about 80 and 250 kPaabsolute such that a significant portion of the aromatic compound in theat least a portion of the effluent fed to the first distillation zone,is vaporized.

Catalyst Regenerations

During use, the catalyst becomes deactivated. This deactivation issubstantially reversible and thus the catalyst can be regenerated.Without intending to be limited to theory, it is believed that asignificant portion of the deactivation occurs through the deposit ofdeactivating components on the catalyst and in its pore structure.Hence, when using two or more selective alkylation reactors, at leastone is on-stream where alkylation occurs and at least one off-streamwhere catalyst regeneration takes place. Regeneration is effected bycontacting the catalyst in the off-stream reactor with a streamcomprising benzene.

After a reactor has been taken off-stream but before catalystregeneration begins, the catalyst is typically purged, or flushed, toremove at least some of the unreacted monoolefins, paraffins, andalkylbenzene from the void volume of the now off-stream reactor. Thepurging conditions are not critical and may be any conditions that areeffective for at least partially purging the void volume of thealkylation catalyst. Preferably the off-stream reactor purgingconditions comprise at least a partial liquid phase.

The contacting conditions for purging the catalyst in the off-streamreactor can be the same throughout the off-stream reactor purging,although some changes could be made. The purging can be started bysimply stopping the flow of the olefinic feed stream to the on-streamreactor, thereby taking the on-stream reactor off-stream. The contactingtemperature is preferably low enough that the deactivating components onthe catalyst are not removed. The temperature is usually between about120° C. and about 170° C. The duration of the purge step can varywidely. The purging need not be complete prior to entering thesubsequent step of ramping the temperature up to a suitable regenerationtemperature. Often, the duration of the purge step will be determined bythe use of the benzene from the purge step and by the cycle time forregeneration that is available. See, for instance, U.S. Pat. No.6,740,789, herein incorporated by reference in its entirety.

After purging, catalyst regeneration can begin. The catalystregeneration conditions are not critical to the success of thisinvention. The regeneration conditions can be any conditions that areeffective for at least partially reactivating the alkylation catalyst.Although olefins may contact the catalyst bed during regeneration,preferably no olefins contact or pass to the catalyst duringregeneration. Preferably the regeneration conditions comprise at least apartial liquid phase.

The contacting conditions can be the same throughout the regeneration,but typically some changes in conditions are made. Commonly, thecontacting temperature is changed during regeneration.

Typically a heating stage is used to increase the temperature to thatsuitable for regeneration. Generally, the temperature is raised by fromabout 50° C. to about 200° C. above the temperature of the purging.Typically the regeneration is conducted at a temperature between about200° C. and about the critical temperature of benzene, and preferablybetween about 220° C. and 270° C. The temperature may be ramped upsteadily or can be increased step-wise with temperature holds. Anysuitable method may be used to raise the temperature. One method isheating the benzene by indirect heat exchange and then passing it intothe reactor.

As the temperature increases, the benzene-containing stream begins toremove deactivating components that accumulated on the surface of thecatalyst and block reaction sites. Since some of the components aregum-like materials that have some color (i.e., are color bodies), thepresence of these materials in the regeneration effluent may begin tolower its Saybolt color.

Once the desired temperature for regeneration is reached, usually a holdperiod follows. The period of time for the regeneration depends on thenature of the catalyst and the extent and nature of the catalystdeactivation, typically from about 2 to about 20 hours. As the catalystbecomes depleted in the deactivating components, the amount andconcentration of these materials in the spent benzene regeneratingstream will decline. The regeneration is typically deemed complete whenthe content of the deactivating components in the spent benzeneregeneration stream drops to a relatively low level.

Finally the reactor is a cooled down. The inlet regeneration temperatureis reduced from the temperature at the end of the second step to thealkylation temperature. The manner and rate of temperature decrease isnot critical to the success of this invention. The temperature may beramped down steadily or dropped step-wise with temperature holds.

Refining

The alkylbenzene effluent from an alkylation reactor generally has thecomponents and concentrations as set forth in Table 1.

TABLE 1 Typical Concentration Component Concentration (weight) (weight)Alkylbenzene 0.05 to 30%   2 to 25% Benzene 33 to 99% 40 to 75%  Totalolefin 0.00001 to 2%     0.0001 to 1%     Total paraffin  0 to 66% 1 to50% Heavies 0.001 to 10%   0.5 to 2%  

Typically refining of the alkylbenzene product involves the use of abenzene distillation, a paraffin distillation and a heavy alkylatedistillation, the benzene distillation is generally conducted with abottoms temperature of less than about 300° C., preferably less thanabout 275° C., usually between about 230° and 270° C., and at a pressureat which the overhead is provided of between about 5 and 300, preferablybetween about 35 and 70, kPa gauge. The overhead generally contains lessthan about 2, preferably less than about 1.5, weight percent paraffins.The benzene distillation assembly may comprise one or more distillationcolumns. More than one overhead may be obtained from the benzenedistillation assembly. For instance, a highly pure stream may beobtained for process needs such as regenerating catalysts or sorbents,e.g., having a paraffin concentration less than about 1, preferably lessthan about 0.1, weight percent. A lesser purity overhead may be obtainedfrom the benzene distillation assembly, e.g., as a side draw, for use asa recycle to the alkylation reaction.

Each column may contain any convenient packing or distillation trays,but most often trays such as sieve and bubble trays, are used. Often theassembly provides at least about 5, say 6 to 70, and preferably 20 to50, theoretical plates. The reflux ratio (herein defined as thedistillate to reflux weight ratio) is often in the range of about 2:1 to1:10, preferably about 1.5:1 to 1:5. The bottoms stream from the benzenedistillation generally contains less than about 1000 ppmw, preferablyless than about 50 ppmw, and sometimes less than about 5 ppmw, benzene.The benzene distillation may occur in a single column or two or moredistinct columns may be used. For instance, a stripping column may beused to remove a portion, e.g., 20 to 50 percent, of the benzene andthen the bottoms from the stripping column would be subjected torectification in a subsequent column to obtain the desired separation.

The paraffin distillation is generally conducted with a bottomstemperature of less than about 300° C., preferably less than about 275°C., usually between about 250° C. and 275° C., and at a pressure atwhich overhead is provided of between about 5 and 110, preferablybetween about 10 and 50, kPa absolute. The column may contain anyconvenient packing or distillation trays, but most often sieve trays areused. Often the paraffins distillation assembly provides at least about5, say 7 to 20, theoretical plates. The reflux ratio is often in therange of about 3:1 to 1:10, preferably about 1:1 to 1:3. The bottomsstream from the paraffins distillation generally contains less thanabout 10, preferably less than about 5, weight percent paraffins andpreferably less than about 10, often less than about 1, ppmw benzene.Preferably, the bottoms stream contains between about 0.5 and 5, sayabout 1 to 5, weight percent paraffins. The paraffins distillation mayoccur in a single column or two or more distinct columns may be used.

The heavy alkylate distillation is generally conducted with a bottomstemperature of less than about 300° C., preferably less than about 275°C., usually between about 250° C. and 275° C., and at a pressure ofbetween about 0.5 and 30, preferably between about 1 and 5, kPaabsolute. The column may contain any convenient packing or distillationtrays, but most often structured packing is used. Often the heavyalkylate distillation assembly provides at least about 5, say 10 to 30,and preferably 10 to 20, theoretical plates. The reflux ratio is oftenin the range of about 2:1 to 1:5, preferably about 0.2:1 to 1:1. Theoverhead from the heavy alkylate distillation generally contains lessthan about 2 weight percent, preferably less than about 1 weightpercent, and sometimes less than about 0.1 weight percent, totalheavies. The benzene content of the overhead stream is generally lessthan about 5, preferably less than about 1, ppmw and the paraffinscontent is often less than about 10 weight percent.

In some instances a finishing distillation may be used where alights-containing overhead stream is provided, it is not essential thatthe paraffin distillation substantially remove all the paraffin from thealkylbenzene stream. Hence opportunities exist for energy savings. Forinstance, the amount of reboiler heat can be reduced as the internalreflux in the distillation column need not be as great as when thebottoms stream has a lesser concentration of paraffins. Also, for agiven column, the capacity of the column can be increased, e.g., todebottleneck an existing refining system.

With respect to the heavy alkylate distillation column, the finishingcolumn can remove, as a bottoms stream, heavies. Therefore the heavyalkylate column can be operated to permit significant amounts of heaviesto be in the overhead. As with the paraffins distillation, theflexibility provided by these processes enables a reduction in reboilerduty for the heavy alkylate distillation. This reduction, in turn,reduces the reflux in the column thereby allowing more heavies to passinto the overhead stream. In addition to the reduction in reboiler heatduty that could be achieved, the capacity of a given distillation columncan be increased.

The finishing distillation is generally conducted with a bottomstemperature of less than about 300° C., preferably less than about 275°C., usually between about 250° C. and 275° C., and at a pressure ofbetween about 5 and 110, preferably between about 10 and 50, kPaabsolute. The assembly may contain any convenient packing ordistillation trays, but most often structured packing is used. Often theassembly provides at least about 2, say 5 to 20, theoretical plates. Themid-cut is generally taken from a point where at least 2, often at least3, theoretical plates exist above and at least 2, often at least 3,theoretical plates exist below. Preferably the distillation assembly isa divided wall column or has an internal column with a dedicatedreboiler. The finishing distillation assembly may also be two separatecolumns.

In some instances it may be desired to subject an alkylbenzene streamthat contains olefinic components to a catalytic operation to improvebromine index, the alkylbenzene stream is passed to a catalyticconversion zone containing an acidic catalyst under olefin reductionconditions. The particular unit operation is not critical to the broadaspects of the invention and any suitable operation may be used.

A number of processes for improving the quality of alkylbenzenes andreducing olefin content have been proposed. The catalysts may be clay ormolecular sieve (natural or synthetic). Included in the clays aresmectites, laponite, saponite, and pillared clays. Filtrol F-24(Engelhard Corporation, Iselin, N.J.) is a preferred clay. Molecularsieves include zeolites A, beta, L, S, T, X and Y and omega, mordenite,erionite, chabazite, boggsite, cloverite, gmelinite, offretite, pentacilmolecular sieves having silica to alumina ratios greater than about 10,and SAPO (such as SAPO 5 and 41). Engelhard Corporation represents thatFiltrol F-24 has a pH of about 3.5.

The bromine index reduction is typically conducted at temperaturesbetween about 25° C. and 250° C., and most often between about 70° C.and 150° C., under a pressure sufficient to maintain the stream underliquid conditions, e.g., within the range of about 0.1 to 150 kPaabsolute. The contact time with the catalyst is sufficient to providethe desired reduction in bromine index. For a fixed bed system, theweight hourly space velocity is typically in the range of about 0.1 to20 hr⁻¹. The bromine index of the treated alkylbenzene stream ispreferably below about 10. The bromine index reduction conditions alsocause byproducts such as the formation of dialkylbenzene and benzenefrom alkylbenzene and form oligomers and polymers from olefiniccomponents.

The effluent from the bromine index reduction is subjected to the fourthdistillation to remove as an overhead, benzene, and heavies such as thedialkylbenzene and the oligomers and polymers from olefinic components.

Transalkylation

The bottoms from the heavy alkylate column can be recovered and used asa heavy alkylate product, or can be subjected to a further separation,e.g., by distillation to recover alkylbenzene contained therein, or canbe subjected to a transalkylation in the presence of benzene to convert,e.g., dialkylbenzenes to monoalkylbenzene.

The transalkylation can be continuous or batch (semicontinuous). Thetransalkylation conditions including catalyst can vary widely. Typicalcatalysts include those having acidic functionality. Acidic catalystscomprise zeolites having a zeolite structure type selected from thegroup consisting of FAU, BEA, MOR, MTW, and NES. Such zeolites includemordenite, ZSM-4, ZSM-12, ZSM-20, ZSM-38, MCM-22, MCM-36, MCM-49, UZM-8,offretite, gmelinite, zeolite Y, NU-87, and gottardite. Another class ofacidic, solid catalyst components are acidified refractory oxides suchas chlorided, fluorided, or sulfated alumina, gallia, boria, molybdia,ytterbia, titania, chromia, silica, zirconia, and the like andcombinations thereof. Clays such as beidellite clays, hectorite clays,laponite clays, montmorillonite clays, nontonite clays, saponite clays,bentonite clays and mixtures thereof and amorphous catalysts may alsofind utility.

If desired, the transalkylation catalyst may be metal stabilized. Themetal component typically is a noble metal or base metal. The noblemetal is a platinum-group metal is selected from platinum, palladium,rhodium, ruthenium, osmium, and iridium. The base metal is selected fromthe group consisting of rhenium, tin, germanium, lead, cobalt, nickel,indium, gallium, zinc, uranium, dysprosium, thallium, and mixturesthereof. The base metal may be combined with another base metal, or witha noble metal. Preferably the metal component comprises rhenium.Suitable metal amounts in the transalkylation catalyst range from about0.01 to about 10 mass-percent, with the range from about 0.1 to about 3mass-percent being preferred, and the range from about 0.1 to about 1mass-percent being highly preferred. In some instances, it may bedesirable to modify the catalyst such as by sulfiding either in-situ orex-situ.

The catalyst may contain suitable binder or matrix material such asinorganic oxides and other suitable materials. The relative proportionof molecular sieve or other catalytically active component in thecatalyst may range from about 10 to about 99 mass-percent, with about 20to about 90 mass-percent being preferred. A refractory binder or matrixcan be used to facilitate fabrication of the catalyst, provide strengthand reduce fabrication costs. The binder should be uniform incomposition and relatively refractory to the conditions used in theprocess. Suitable binders include inorganic oxides such as one or moreof alumina, magnesia, zirconia, chromia, titania, boria and silica. Thecatalyst also may contain, without so limiting the composite, one ormore of (1) other inorganic oxides including, but not limited to,beryllia, germania, vanadia, tin oxide, zinc oxide, iron oxide andcobalt oxide; (2) non-zeolitic molecular sieves, such as thealuminophosphates of U.S. Pat. No. 4,310,440, thesilicoaluminophosphates of U.S. Pat. No. 4,440,871 and ELAPSOs of U.S.Pat. No. 4,793,984; and (3) spinels such as MgAl₂O₄, FeAl₂O₄, ZnAl₂O₄,CaAl₂O₄, and other like compounds having the formula MO—Al₂O₃ where M isa metal having a valence of 2; which components can be added to thecomposite at any suitable point.

The transalkylation is conducted in the liquid phase with a benzene tototal alkyl substituted benzenes ratio (Bz:TAB) of at least about 1:1.Often this ratio is between about 2:1 to 100:1. In general, higherBz:TAB is preferred as the liquid flow assists in removing cokeprecursors from the catalyst, thereby enhancing time on stream prior toregeneration or replacement. Preferred Bz:TAB will depend upon theseverity of the transalkylation conditions, the superficial liquidvelocity in the catalyst bed and the conversion per pass. Typically, theBz:TAB is within the range of about 20:1 to 100:1, say, 30:1 to 80:1.The source of the benzene is not critical in the broad aspects. Thesources of benzene include fresh benzene, benzene obtained from therefining section, benzene obtained from regeneration of the alkylationcatalyst, benzene obtained from the regeneration of a solid sorbent suchas used to treat the olefin-containing feedstock, and benzene recycledwithin the transalkylation unit operation itself. Where the benzene is aspent regeneration stream, the stream may be used directly or may besubjected to a purification to remove undesirable components such asgums and coke precursors from the regeneration of solid sorbent. Thepurification may be a selective sorption, membrane separation or,preferably, a distillation. Advantageously, adequate purification via adistillation may be obtained by a flash distillation or one containingrelatively few theoretical distillation plates and low reflux to feedratios.

Conditions employed for transalkylation normally include a temperatureof from about 130° C. to about 270° C., preferably from about 180° C. to240° C. At higher temperatures, a greater amount of cracking occurs withincreased co-production of lights, i.e., aliphatic hydrocarbons having 9and fewer carbon atoms. Also, the higher temperatures tend to result inloss of linearity of the alkylbenzene which is not desirable foralkylbenzenes to be used for sulfonation to detergents. Hence, the morepreferred transalkylation temperatures are from about 190° C. to 220° C.Moderately elevated pressures broadly ranging from about 100 kPa to 10MPa absolute are also used for transalkylation such that the reactantsremain in the liquid state.

The transalkylation reaction can be effected over a wide range of spacevelocities, with higher space velocities enhancing the stability of thecatalyst but at the expense of conversion of dialkylbenzenes tomonoalkylbenzene. Often, the conversion of dialkylbenzenes in the feedto a transalkylation zone is less than about 60 mass percent, say,between about 20 and 50 mass percent. Weight hourly space velocitygenerally is in the range of from about 0.1 to about 30, and frequentlybetween about 5 and 25, hr⁻¹. The adding of hydrogen is optional. Ifpresent, free hydrogen is associated with the feedstock and recycledhydrocarbons in an amount of about 0.1 moles per mole of TAB up to about10 moles per mole of TAB.

For purposes herein, a catalyst bed is termed a reactor whether in thesame or a separate vessel from another bed. The catalyst may be used asa packed bed or a fluidized bed. The feed to the reaction zone may bepassed either upflow or downflow, or even horizontally as in a radialbed reactor. In one desirable variant, olefin-containing feedstock maybe fed into several discrete points within the reaction zone.

One or more transalkylation zones can be used. The transalkylation zonesmay be configured in parallel with the same or different catalyst ineach. A preferred transalkylation process effectively uses the benzeneby separating at least a portion of the benzene from at least onetransalkylation zone and passing that benzene to one or moretransalkylation zones as all or a part of the benzene. The separation,if by distillation, will result in some of the lights also beingrecycled and a continuous or intermittent purge may be required tomaintain the lights at a suitable concentration, e.g., less than about20, preferably less than about 10, volume percent of the separatedbenzene. Preferably the fraction containing the alkylbenzene will alsocontain benzene to assist in maintaining a steady state operation. Oneadvantage with this preferred process using a separation unit operationassociated with the transalkylation zone is that the amount of freshbenzene required is reduced while still being able to provide a highBz:TAB.

With respect to the associated separation being a distillation(transalkylation distillation), the amount of effluent from one or moretransalkylation zones that is directed to the transalkylationdistillation may be as little as 20 weight percent of the total effluentor may comprise the entire effluent stream. Often at least about 50, andsometimes at least about 80, weight percent of the effluent is subjectedto the transalkylation distillation. Where more than one transalkylationzone is used, the effluent from one or more of the zones can be fed tothe transalkylation distillation.

In any event, sufficient fluid must be removed from the transalkylationzone and the transalkylation distillation loop to prevent an unduebuild-up of inerts or other impurities in the loop. Typically theconcentration of lights in the alkylation zone is less than about 20weight percent, and preferably less than about 10, weight percent. Onlya portion of the benzene contained in the feed to the transalkylationdistillation zone is intended to be recovered in the overhead. Theamount of the aromatic compound recovered in the overhead is oftenbetween about 20 and 98, say, 50 to 70 or 90, weight percent of that inthe distillation feed. The overhead may also contain lights.

Advantageously, the distillation equipment need not be extensive toachieve such recovery, e.g., the distillation may be accomplished withless than about 5 theoretical plates. Moreover, the lights distillationis preferably conducted without significant reboiler heat. Preferablythe sought recovery of benzene is accomplished by a flash distillationdue to temperature of the effluent from the transalkylation zone withoutthe need for a heat source. Where heat is supplied to thetransalkylation distillation, e.g., to provide for internal reflux in afractionation column, it preferably is less than about 40, morepreferably less than about 30, kilocalories per kilogram of the feed tothe transalkylation distillation. Where a reflux is used, the rate ofexternal reflux (distillation feed to reflux, F/R) is preferably betweenabout 0.1:1 to 2:1, more preferably between about 0.4:1 and 0.8:1,kilogram per kilogram of effluent fed to the transalkylationdistillation zone.

The transalkylation distillation may be effected in an open vessel for aflash distillation or may contain suitable trays or packing for afractionation. A flash distillation may contain a demister to preventliquid carryover in the overhead. Heat to the lights distillation zonemay be provided by indirect heat exchange at the bottom of the zone, orby withdrawing, heating and recycling to the base of the column aportion of the liquid contained at the bottom of the lights distillationzone. The transalkylation distillation will provide a higher boilingfraction containing alkylbenzene, heavies and benzene.

All or a portion of the transalkylation product (obtained either or bothfrom the transalkylation zone or the separation) is passed to thebenzene column of the refining section. Unreacted heavies, of course,will be recovered in the refining section and can be thus recycled tothe transalkylation unit operation. Where the transalkylation isoperated to achieve a low conversion per pass, say, 20 to 40 weightpercent conversion of the dialkylbenzenes, a portion of thetransalkylation product (obtained either or both from thetransalkylation zone or the separation) can be passed to atransalkylation zone for further conversion. Since low conversion isacceptable, lower temperatures can be used to enhance the linearity ofthe alkylbenzene produced by the transalkylation.

Rough Distillation of Spent Regenerant

In the processes of this invention, spent regenerant containing benzeneand deactivating components is subjected to rough distillation toprovide a benzene-containing stream having less than about 1, preferablyless than about 0.5, mass percent hydrocarbons containing at least 12carbon atoms. Without being limited to theory, it is believed thatdeactivating components on solid alkylation catalyst comprise highermolecular weight species. The hydrocarbon species may be aliphatic oraromatic.

A rough distillation is a distillation using up to 2, preferably up to1, theoretical distillation plates. Where a reflux is used, the refluxratio is preferably less than about 1:1, most preferably less than about0.5:1. Most advantageously, the rough distillation is a flashdistillation. Especially where the spent regenerant is at a temperatureof at least about 170° C., preferably at least about 200° C., as wouldbe the spent regenerant from the regeneration of a solid alkylationcatalyst or a transalkylation catalyst, no reboiler duty may be requiredto effect the separation. The fractionation may be conducted by reducingthe pressure of the spent regenerant, say, to less than about 200,preferably less than about 130, kPa absolute. In general, the roughdistillation is conducted at a bottoms temperature in the range of about150° C. to 20° C., and a pressure of from about 10 to 500, preferably 50to 200, kPa absolute.

The rough distillation may or may not be conducted in the presence ofsuitable packing or trays. Where a flash distillation is used, often ademister or other vapor/liquid separator is used to minimize carry overliquid in the benzene stream.

The rough distillation is preferably conducted such that at least somebenzene is contained in the bottoms stream. The amount of benzenepresent in the higher boiling fraction can fall within a wide rangedepending upon the desired operation. For instance, greater amounts ofbenzene may be desired where either the concentration of deactivatingcomponents in the spent regenerant is very low, or where components arepresent that have normal boiling points near and above that of benzene,and it is sought to remove a greater portion of these components withthe higher boiling fraction. In some instances, the mass ratio ofbenzene to hydrocarbons having at least 12 carbon atoms may be as greatas 50:1 or more. On the other hand, over the entire regeneration cycle,generally benzene is present in the higher boiling fraction in an amountless than about 70, preferably less than about 50, mass percent.

In preferred aspects of this invention, the spent regenerant provided tothe rough distillation is from at least one of a regeneration of thesolid alkylation catalyst or, if used, a transalkylation catalyst. Andmost preferably, in the aspects of this invention where the benzenestream from the rough distillation is used for regeneration of acatalyst or solid sorbent. the spent regenerant contains little, if any,say, less than about 1, preferably less than about 0.1, mass percentparaffin. This low paraffin-containing spent regenerant is thus thatobtained after a purge step in the regeneration of the catalyst,especially the alkylation catalyst where paraffin is present in asignificant amount. Where a continuous supply of a benzene stream fromthe rough distillation is sought, it may be desirable to provide astorage tank to enable a constant feed of spent regenerant to beprovided to the rough distillation.

All or a portion of the benzene stream from the rough distillation maybe used for one or more catalyst or sorbent regenerations or for feed tothe alkylation reactor. As stated above, a preferred embodiment of theprocesses of this invention entails providing a second benzene loop inthe alkylbenzene facility where the benzene stream from the roughdistillation is recycled for catalyst regeneration. To the extent thatbenzene from the benzene column of the alkyl benzene refining system isused, it would be as make-up to replace that benzene lost from thesecond loop, e.g., by a purge or with the higher boiling fraction fromthe rough distillation. The higher boiling fraction from the roughdistillation can be disposed of or used in any convenient manner.

THE DRAWINGS

The drawings are provided in illustration of an embodiment of theinvention and are not in limitation thereof.

FIG. 1 schematically depicts an alkylbenzene complex 100 including thedehydrogenation of paraffin feedstock to make the olefin-containingfeedstock for the alkylation. As shown, paraffin feedstock is suppliedvia line 102 to olefin production unit 104. Olefin production unitdehydrogenates paraffin and yields an olefin-containing feedstock whichis withdrawn via line 106. Within olefin production unit 104 is not onlya dehydrogenation reactor but also a distillation refining system and aselective hydrogenation unit operation to eliminate diolefins. Theolefin-containing feedstock in line 106 contains predominantlyparaffins, about 10 to 15 volume percent olefins and other co-boilinghydrocarbons including aromatics. Thus the feedstock is passed toselective sorption unit 108 for removal of aromatic impurities. Theselective sorption unit 108 may be of any suitable design such asdisclosed above. The selective sorption unit uses solid sorbent whichcan be regenerated with a benzene stream as will be discussed later.

The treated olefin-containing feedstock is then passed via line 110 toalkylation reaction assembly 112. Alkylation reaction assembly isdiscussed in connection with FIG. 2. In FIG. 2, the olefin-containingfeedstock in line 110 is passed to olefin header 114 and then to controlvalve assemblies 116 a, 116 b and 116 c associated with reactors 118 a,118 b and 118 c. Control valve assemblies may be one or more valves tocontrol flows into and out of each reactor.

Benzene is supplied via line 120 to benzene header 122 which is in flowcommunication with each of control valve assemblies 116 a, 116 b and 116c. Each of control valve assemblies 116 a, 116 b and 116 c are in fluidcommunication with reactors 118 a, 118 b and 118 c, respectively vialines 124 a, 124 b and 124 c. Reactors 118 a, 118 b and 118 c are influid communication with the next sequential control valve assembly 116b, 116 c and 116 d, respectively via lines 126 a, 126 b and 126 c. Eachof control valve assemblies 116 a, 116 b, 116 c and 116 d are in fluidcommunication with internal flow header 128. Internal flow header 128allows for the passage of a reactor effluent from one reactor to theinlet for another reactor. Each of control valve assemblies 116 b, 116 cand 116 d are in fluid communication with alkylation effluent header 130which in turn is in communication with line 132 for withdrawingalkylation effluent from alkylation reaction assembly 112. Each ofcontrol valve assemblies 116 b, 116 c and 116 d are also in fluidcommunication with spent benzene header 134 which in turn is incommunication with line 136 for withdrawing spent benzene fromalkylation reaction assembly 112.

In operation, alkylation reactor assembly permits two reactors to besequentially on stream while one reactor is undergoing regeneration andpermits any of the reactors to be the first reactor in the series onstream. By way of illustration, olefin-containing feedstock in header114 is partitioned by valve assemblies 116 a, 116 b and 116 c to providea portion of the feedstock only to reactors 118 a and 118 b. Withreactor 118 a being the first in the series, the control valveassemblies provide for benzene for the alkylation reactor to be allintroduced into reactor 118 a. Thus control valve assembly 118 b permitsno benzene from benzene header 122 from entering into reactor 118 b.However, control valve assembly 116 c permits benzene at a rate suitablefor regeneration to be introduced into reactor 118 c. The effluent fromreactor 118 a passes via line 126 a to control valve assembly 116 b. Asreactor 118 b is the next reactor in series, the effluent is directedvia line 124 b to reactor 118 b. Control valve assembly directs theeffluent from reactor 118 b which is conveyed by line 126 b toalkylation effluent header 130 to be withdrawn from reactor assembly 112via line 132. Reactor 118 c is undergoing regeneration and the spentbenzene regenerant is passed via line 126 c from reactor 118 c tocontrol valve assembly 116 d which directs it to benzene purge header134 and withdrawal from alkylation reactor 112 via line 136.

Upon completion of the regeneration of the catalyst in reactor 118 c, itis placed back on-line and one of the other reactors is taken out ofservice for catalyst regeneration. Typically, the second reactor in theseries on line is transitioned to regeneration. In such event, reactor118 c becomes the first reactor in the series and reactor 118 a becomesthe second in series. The control valve assembly appropriately changesthe flows of the various streams. Thus, the benzene for the alkylationreaction is passed through valve assembly 116 c and line 124 c toreactor 118 c while no benzene passes through valve assembly 116 a.Benzene for regeneration is passed through valve assembly 116 b and line124 b to reactor 118 b. Olefin-containing feedstock is partitionedbetween valve assemblies 116 a and 116 c. The effluent from reactor 118c is passed via line 126 c to valve assembly 116 d to internal flowheader which directs the effluent to valve assembly 116 a to be passedto reactor 118 a. Valve assembly 116 b directs the effluent from reactor118 a to alkylation effluent header 130. The effluent from reactor 118b, which is being regenerated, is directed by valve assembly 116 c tobenzene purge header 134.

As can be seen from the above, each of the reactors can be cycled todifferent positions while on stream and taken off-stream forregeneration.

Returning to FIG. 1, alkylation effluent from reactor assembly 112 ispassed via line 132 to benzene column 138 to provide abenzene-containing fraction which is recycled via line 120 to reactorassembly 112. Fresh benzene is provided via line 140 to benzene column138. Not shown, but optional uses for the benzene-containing fractionfrom benzene column 138 is as a feed to the transalkylation reactionsystem and as a regenerant for the solid sorbent in selective sorptionunit 108.

The bottoms fraction from benzene column, which contains alkylbenzene,heavies and paraffin is passed via line 142 to paraffins column 144. Alower boiling fraction rich in paraffins is passed via line 146 toolefin production unit 104. The bottoms fraction of paraffins column144, which contains alkylbenzene and heavies is passed via line 148 toheavy alkylate column 150. Heavy alkylate column 150 provides a lowerboiling fraction rich in alkylbenzene that is withdrawn via line 152.This fraction may also contain some benzene and paraffins as well assome olefinic components and thus a clay treater and finishing columnare used. As shown, the lower boiling fraction in line 152 is passed toclay treater 154 and then via line 156 to finishing column 158. A sidedraw from finishing column 158 is taken via line 160 which is thealkylbenzene product. An overhead fraction containing paraffin andbenzene is passed via line 162 to line 146 for ultimate recycling toolefins production unit 104. The bottoms fraction from finishing column158 contains dialkylbenzene and is passed via line 164 for combinationwith the bottoms fraction from heavy alkylate column 150 which iswithdrawn via line 166. The bottoms fraction from the heavy alkylatecolumn contains heavies, i.e., dialkylbenzene, other heavier aromaticsand olefin oligomers, and some alkylbenzene. The combined stream passesto transalkylation assembly 168. A stream may be split off via line 198either as a purge to prevent undue build-up of heavy hydrocarbons or forfurther refining to provide a dialkylbenzene-containing product.

Returning to alkylation reactor assembly 112, spent benzene regenerant,which contains benzene as well as deactivating components removed fromthe catalyst, is passed via line 136 to distributor assembly 170. Whilenot essential, distributor assembly directs the spent benzene regenerantthat contains little color formers and gums directly to transalkylationassembly 168 via line 172. This spent benzene is from a purge of thereactor undergoing regeneration and thus contains alkylbenzenes,paraffin, and dialkylbenzene from the interstitial regions and from thecatalyst surface and possibly some of the regenerant as the reactorcools down to temperatures suitable for alkylation. As the color formersand gums start to be removed from the regenerating catalyst, distributor170 directs the spent benzene regenerant to hold tank 174 via line 176.Hold tank 174 serves as a reservoir for the spent benzene regenerantfrom which a constant flow of benzene can be withdrawn via line 178 fordistillation in column 180.

A bottoms fraction containing higher molecular weight color formers anddeactivating components is withdrawn via line 182 from column 180. Abenzene fraction is withdrawn via line 184. As shown, a portion of thebenzene fraction in line 184 is directed to selective sorption unit 108as regenerant and to reaction assembly 112 where it can be used for oneor both of regeneration and benzene feed for the alkylation reaction.The spent regenerant from selective sorption unit 108 is passed via line186 to hold tank 174.

A portion of the benzene fraction in line 184 is passed via line 188 tovalve assembly 190 which can direct all or part of the stream via line192 to line 172 for the transalkylation assembly 168 and all or part ofthe stream via line 194 to line 196 which is in communication withbenzene column.

Transalkylation assembly 168 is described further with reference to FIG.3. The combined bottoms fraction from heavy alkylate column 150 and fromfinishing column 158 is passed to transalkylation assembly 168 via line166, and a portion of the stream is directed to each of reactors 200 and202 via lines 204 and 206, respectively. The make-up benzene is suppliedby line 172 to line 204 and is passed to transalkylation reactor 200.The transalkylation effluent is withdrawn from reactor 200 via line 208and supplied to stripping column 210 which serves to provide abenzene-containing fraction in line 212. A purge of thebenzene-containing fraction can be effected via line 214. This purge canbe passed to the benzene column, used for fuel value or exhausted fromthe complex. As shown, a portion of the benzene-containing fraction canbe recycled, if desired, to reactor 200. The balance of this fraction ispassed via line 218 to serve as the benzene for the transalkylation inreactor 202. Alternatively, part of the make-up benzene in line 172 canbe passed to reactor 202. The effluent from reactor 202 is passed vialine 220 to stripping column 210.

The bottoms fraction from stripping column 210 contains alkylbenzeneproduced by the transalkylation, unreacted dialkylbenzene, other heaviesand a portion of the benzene. The bottoms fraction is withdrawn via line196 and passed to benzene column 138 where benzene is recovered. Theremaining unit operations in the refining section recover alkylbenzene,paraffin and return dialkylbenzene to the transalkylation assembly. Ifdesired, a stream can be removed from line 196 and recycled to reactors200 and 202 via lines 222 and 224, respectively for further conversionof unreacted dialkylbenzene.

1. A continuous, integrated process for preparing linear alkylbenzenesby the alkylation of benzene with olefin having between about 8 and 16carbon atoms, said olefin being contained in admixture with paraffin, inthe presence of regenerable, solid, acid alkylation catalyst comprising:a. continuously supplying benzene and a mixture of said olefin andparaffin to alkylation conditions in at least one alkylation zone of atleast two alkylation zones including the presence of a catalyticallyeffective amount of said catalyst to provide an alkylation productcontaining alkylbenzene, dialkylbenzene, and unreacted benzene, whereinsaid alkylation deactivates said catalyst, wherein the catalyst isselected from the group consisting of zeolytes, acidified refractoryoxides, and mixtures thereof; b. providing the alkylation product to afirst separator and separating benzene from the alkylation product toprovide a benzene-rich fraction, at least a portion of which is recycledto step (a), and a substantially benzene-free fraction containingalkylbenzene and paraffin; c. separating paraffin from saidsubstantially benzene-free fraction to provide a paraffin-rich fractionand a substantially paraffin-free fraction containing alkylbenzene anddialkylbenzene; d. periodically regenerating said catalyst in at leastone of said alkylation zones by continuously passing through said zone,benzene under regeneration conditions to provide a spentbenzene-containing regeneration stream which also contains deactivatingcomponents removed from the catalyst; e. providing the spentbenzene-containing regeneration stream to a second separator andfractionating at least a portion of the spent benzene-containingregeneration stream by crude distillation of benzene from deactivatingcomponents to provide a lower boiling benzene stream containing lessthan about 1 mass percent hydrocarbons having at least 12 carbon atoms;f. separating the substantially paraffin-free fraction of step (c) toprovide an alkylbenzene fraction substantially devoid of dialkylbenzenesand a heavies fraction containing dialkylbenzenes; and g. providing atleast a portion of the heavies fraction to transalkylation conditionscomprising the presence of a catalytically effective amount of solidtransalkylation catalyst and benzene, at least a portion of which isprovided from the lower boiling benzene fraction from step (e), toprovide a transalkylation product containing alkylbenzene and unreactedbenzene; wherein the mixture of olefin and paraffin of step (a) isderived from the dehydrogenation of paraffin and a selective sorbent isused to remove aromatic compounds from the olefin and paraffin mixtureprior to step (a) and at least a portion of the lower boiling benzenestream from step (e) is used to regenerate the selective sorbent andprovide a spent regenerant stream.
 2. The process of claim 1, wherein atleast a portion of the lower boiling benzene stream from step (e) ispassed to step (b).
 3. The process of claim 1, wherein thetransalkylation deactivates the transalkylation catalyst, thetransalkylation catalyst is periodically regenerated by contact with astream containing benzene to provide a spent benzene-containing streamcontaining deactivating components, and at least a portion of thebenzene for the regeneration stream is at least a portion of the lowerboiling benzene fraction from step (e).
 4. The process of claim 3,wherein at least a portion of the spent benzene-containing stream fromregenerating the transalkylation catalyst is passed to step (e).
 5. Theprocess of claim 1, wherein at least a portion of the lower boilingbenzene stream from step (e) is passed to step (a).
 6. The process ofclaim 1, wherein at least a portion of the lower boiling beuzene streamfrom step (e) is passed to step (d).
 7. The process of claim 1, whereinthe regeneration of step (d), which includes a spent benzene-containingregeneration stream, comprises (i) a purge stage during which thecatalyst is flushed, (ii) a heating stage during which the temperatureis increased to that suitable for regeneration, (iii) a regeneratingstage during which deactivating components are removed from thecatalyst, and (iv) a cool down stage during which the catalyst is cooledto a temperature suitable for use in step (a), and wherein at least thespent benzene-containing regeneration stream used in step (iii) ispassed to step (e).
 8. The process of claim 7, wherein at least aportion of the spent benzene-containing regeneration stream from step(i) is passed to step (a) without the fractionation of step (e).
 9. Theprocess of claim 7, wherein at least a portion of the spentbenzene-containing regeneration stream from step (i) is used as at leasta portion of benzene feed for a transalkylation of heavies.
 10. Theprocess of claim 7, wherein at least a portion of the spentbenzene-containing regeneration stream from step (iii) is passed to step(e) and the lower boiling benzene stream is used to regenerate aselective sorbent bed.
 11. The process of claim 7, wherein at least aportion of the spent benzene-containing regeneration stream from step(iii) is passed to step (e) and the lower boiling benzene stream is usedto regenerate catalyst.
 12. The process of claim 11, wherein thecatalyst is a solid, acidic alkylation catalyst.
 13. The process ofclaim 7, wherein at least a portion of the spent benzene stream fromstep (iii) is passed to step (3) and the lower boiling benzene stream isused as at least a portion of benzene feed for a transalkylation ofheavies.
 14. The process of claim 1, wherein the fractionating of step(e) provides a higher boiling fraction containing benzene.
 15. Acontinuous, integrated process for preparing linear alkylbenzenes by thealkylation of benzene with olefin having between about 8 and 16 carbonatoms, said olefin being contained in admixture with paraffin, in thepresence of regenerable, solid, acid alkylation catalyst comprising: a.continuously supplying benzene and a mixture of said olefin and paraffinto alkylation conditions in at least one alkylation zone of at least twoalkylation zones including the presence of a catalytically effectiveamount of said catalyst to provide an alkylation product containingalkylbenzene, dialkylbenzene and unreacted benzene, wherein saidalkylation deactivates said catalyst, wherein the catalyst is selectedfrom the group consisting of zeolytes, acidified refractory oxides, andmixtures thereof; b. providing the alkylation product to a firstseparator and separating benzene from the alkylation product to providea benzene-rich fraction, at least a portion of which is recycled to step(a), and a substantially benzene-free fraction containing alkylbenzene,dialkylbenzene, and paraffin; c. separating paraffin from saidsubstantially benzene-free fraction to provide a paraffin-rich fractionand a substantially paraffin-free fraction containing alkylbenzene anddialkylbenzene; d. periodically regenerating said catalyst in at leastone of said alkylation zones by continuously passing through said zonebenzene under regeneration conditions to provide a spentbenzene-containing regeneration stream which also contains deactivatingcomponents removed from the catalyst; e. providing the spentbenzene-containing regeneration stream to a second separator andfractionating at least a portion of the spent benzene-containingregeneration stream by crude distillation benzene from deactivatingcomponents to provide a lower boiling benzene stream containing lessthan about 1, mass percent hydrocarbons having at least 12 carbon atoms;f. passing at least a portion of the lower boiling benzene stream fromstep (e) to step (d); g. separating the substantially paraffin-freefraction of step (c) to provide an alkylbenzene fraction substantiallydevoid of dialkylbenzenes and a heavies fraction containingdialkylbenzenes; and h. providing at least a portion of the heaviesfraction to transalkylation conditions comprising the presence of acatalytically effective amount of solid transalkylation catalyst andbenzene, at least a portion of which is provided from the lower boilingbenzene fraction from step (e), to provide a transalkylation productcontaining alkylbenzene and unreacted benzene; wherein the mixture ofolefin and paraffin of step (a) is derived from the dehydrogenation ofparaffin and a selective sorbent is used to remove aromatic compoundsfrom the olefin and paraffin mixture prior to step (a) and at least aportion of the lower boiling benzene stream from step (e) is used toregenerate the selective sorbent and provide a spent regenerant stream.16. The process of claim 15, A having a first benzene recycle loopcomprising step (a) and step (b) and a second benzene recycle loopcomprising step (d) and step (e).